Charging series before mounting, what voltage?

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italianuser

Member
Joined
Feb 25, 2020
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335
Hi there :giggle:just finished testing/dividing my cells, I have 1120+ which is the amount I need for four 280 cell batteries (14s20p), so I'm happy about that. Took three months to do the job WTH!

These are all the cell types I have, Samsung 22P/22F and Sony UR18650AA (double A) I have the most, but I did check every single cell type to fullfill the "know your cells" requirement (ref. @Wolf -thanks to you bro!).

1627921932122.png


Now, before mounting the series I'll charge all 14s1P blocks to the same voltage. Mounting will start August the 16th when family's on holiday and I'm home alone, me and my lithium addiction:p

My question is this: I see people doing this pre-mounting charge at different voltages, I'd charge them all to 4.20V. I suppose it's ok, is there any reason to charge them lower?
 

Wolf

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Sep 25, 2018
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1,561
Took three months to do the job WTH!
He he 3 months that's nothing, it took me over a year to come up with 1120 good cells. Of course I also processed over 10,000 cells all from used laptop and medical packs with not the best results.
As far as I am concerned once the 20p packs are built you need to test them each for Ah capacity.
That would be a C/D/C cycle, charge to 4.2v discharge to 3.0v and recharge to whatever you want. Just make sure you recharge all of them to the same voltage. 3.8 for storage or 4.0 if you plan on putting them into service soon.
Then you can set them in series and get your BMS set up. If all your 20p packs are the same voltage your BMS will have very little balancing to do if any, especially if all your packs are well matched.
I'd charge them all to 4.20V. I suppose it's ok, is there any reason to charge them lower?
4.2V is OK initially, but for longevity I would recommend running the packs between 4.05 to 3.45.
Wolf
 

italianuser

Member
Joined
Feb 25, 2020
Messages
335
He he 3 months that's nothing, it took me over a year to come up with 1120 good cells. Of course I also processed over 10,000 cells all from used laptop and medical packs with not the best results.
As far as I am concerned once the 20p packs are built you need to test them each for Ah capacity.
That would be a C/D/C cycle, charge to 4.2v discharge to 3.0v and recharge to whatever you want. Just make sure you recharge all of them to the same voltage. 3.8 for storage or 4.0 if you plan on putting them into service soon.
Then you can set them in series and get your BMS set up. If all your 20p packs are the same voltage your BMS will have very little balancing to do if any, especially if all your packs are well matched.

4.2V is OK initially, but for longevity I would recommend running the packs between 4.05 to 3.45.
Wolf
Oh, yes, capacity test before mounting. That will be very time consuming I suppose, especially when I find a lower/higher pack a swap cells in&out and test again. I think I'll test capacity on all packs first then choose where to eventually change cell(s).
 

ziporah

New member
Joined
Apr 26, 2021
Messages
26
I’m just IR testing my 18650aa cells. First 90 processed, avg ir is 41,6 on my cells. I found some spec stating it should be <100m. What are the values from your cells?
image.jpg
 

italianuser

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Joined
Feb 25, 2020
Messages
335
They do look super, don't they! Yes!

Sanyo cells, although we do have quite a few posts speaking bad about them (they heat up a lot), actually seem like good cells to me.

My IR values are similar to yours:

1950-2099mAh, 10 cells, IR 40-49
2100-2199mAh, 73 cells, IR 40-49
2200-2299mAh, 133 cells, IR 40-49
* Liitokala capacity measuments are slightly high from what I read in Wolf's stats

Sanyo1.jpeg Sanyo2.jpeg
 

OffGridInTheCity

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Dec 15, 2018
Messages
1,706
My process is to charge/discharge-test/charge - and let sit. They're ~ 4.15v at that point. After a few weeks measure them for self-discharge and keep all the ones above 4.10v and build the packs.

At this point - if you just build the packs into a battery, they will all be 4.10-4.15v... and no problem just hooking them up as long as 14s = 57.4v is OK at the hookup point.

In my case, I'm typically paralleling in a new 14s battery to the existing bank. My daily is such that its around 3.6v each morning... SO... I use the xCharger X8 to discharge each pack to 3.6v. I love that xCharger can discharge down to a set voltage and auto-shut-off. Then assemble the new packs/battery into the overall battery bank in the morning. Finally, Batrium is used for a post-hookup touchup.
 

ziporah

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Apr 26, 2021
Messages
26
I finished measuring the IR on all 300 cells. This is the IR spread on them.
Next up => charge them all back to top level and test them. will take me a couple of days/weeks again, after my batch of US18650V3 is done.
It feels positive that all cells are in the 36-46 range, that should provide me with some good capacities.
1627936065256.png
 
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